References of "Kaczor, Jakub 2000E941"
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See detailCooperative effects of Janus and Aurora kinase inhibition by CEP701 in cells expressing Jak2V617F
Gäbler, Karoline UL; Rolvering, Catherine UL; Kaczor, Jakub UL et al

in Journal of Cellular & Molecular Medicine (2013), 17(2), 265-276

The Janus kinase 2 mutant V617F occurs with high frequency in myeloproliferative neoplasms. Further mutations affecting the Janus kinase family have been discovered mostly in leukaemias and in ... [more ▼]

The Janus kinase 2 mutant V617F occurs with high frequency in myeloproliferative neoplasms. Further mutations affecting the Janus kinase family have been discovered mostly in leukaemias and in myeloproliferative neoplasms. Owing to their involvement in neoplasia, inflammatory diseases and in the immune response, Janus kinases are promising targets for kinase inhibitor therapy in these disease settings. Various quantitative assays including two newly developed screening assays were used to characterize the function of different small-molecule compounds in cells expressing Jak2V617F. A detailed comparative analysis of different Janus kinase inhibitors in our quantitative assays and the subsequent characterization of additional activities demonstrated for the first time that the most potent Jak2 inhibitor in our study, CEP701, also targets Aurora kinases. CEP701 shows a unique combination of both activities which is not found in other compounds also targeting Jak2. Furthermore, colony forming cell assays showed that Janus kinase 2 inhibitors preferentially suppressed the growth of erythroid colonies, whereas inhibitors of Aurora kinases preferentially blocked myeloid colony growth. CEP701 demonstrated a combined suppression of both colony types. Moreover, we show that combined application of a Janus and an Aurora kinase inhibitor recapitulated the effect observed for CEP701 but might allow for more flexibility in combining both activities in clinical settings, e.g. in the treatment of myeloproliferative neoplasms. The newly developed screening assays are high throughput compatible and allow an easy detection of new compounds with Janus kinase 2 inhibitory activity. © 2012 The Authors. Published by Foundation for Cellular and Molecular Medicine/Blackwell Publishing Ltd. [less ▲]

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See detailJanus kinases as targets for small molecule inhibitors
Kaczor, Jakub UL

Doctoral thesis (2010)

Many cytokines transduce signals by employing receptor/Janus kinase (Jak) complexes that, once activated, promote phosphorylation of several signaling proteins such as STAT transcription factors. The Jak ... [more ▼]

Many cytokines transduce signals by employing receptor/Janus kinase (Jak) complexes that, once activated, promote phosphorylation of several signaling proteins such as STAT transcription factors. The Jak/STAT pathway is normally tightly modulated by regulatory mechanisms preventing its over-activation. However, a number of genetic alterations in Jak kinase genes have been found in myeloproliferative neoplasms and leukemia that render the Jaks hyperactive and cytokine-independent. In the present thesis pharmacologic and genetic approaches were applied to study aspects of both the cytokine-dependent and -independent activation of the Jak/STAT pathway. We applied a chemical genetics approach to Janus kinases and generate analogue-sensitive Jak1 and Jak2 mutants. With these tools we could for the first time specifically inhibit either Jak1 or Jak2 and investigate their relative contributions in IFN signaling. Single inhibition of either Jak by an inhibitor analogue showed differential effects on IFN-mediated STAT1 phosphorylation, Jak2 inhibition having a stronger suppressive effect. Furthermore, we identified STAT1 and IRF1 as genes, whose increased expression upon IFN stimulation strongly depends on active Jak2 but not on Jak1. Most of the IFN-regulated genes, however, depend on both Jak1 and Jak2 activity. Exploiting this quick and reversible pharmacological inhibition of analogue-sensitive kinases we address the temporal requirement of Jak activity and the importance of different phases of the IFN response. Moreover, we further characterized constitutively active Jak2 mutants and show that SOCS proteins seem to be directly involved in their proteasome-mediated degradation. There is an increasing interest in developing small molecule inhibitors targeting Jaks and Jak mutants. We show that Erlotinib, an inhibitor targeting EGFR which is already used in the clinic to treat lung and pancreatic cancer, can have a beneficial additional effect if combined with a Jak-specific inhibitor on cell growth suppression and apoptosis of Jak2-V617F- or Jak3-A572V-positive leukemic cells. Erlotinib, in contrast to Jak inhibitors targeting Jaks directly affects the eIF2/ATF4 pathway in leukemic cells. This is of general interest since Erlotinib treatment in conjunction with other kinase inhibitors could be an interesting approach also in other kinase-dependant leukemias (e.g. BCR-ABL-positive CML). [less ▲]

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See detailHypoxia-inducible factor 1alpha is up-regulated by oncostatin M and participates in oncostatin M signaling
Vollmer, Stefan UL; Kappler, Valérie; Kaczor, Jakub UL et al

in Hepatology (Baltimore, Md.) (2009), 2009(3),

The interleukin-6-type cytokine oncostatin M (OSM) acts via the Janus kinase/signal transducer and activator of transcription pathway as well as via activation of mitogen-activated protein kinases and is ... [more ▼]

The interleukin-6-type cytokine oncostatin M (OSM) acts via the Janus kinase/signal transducer and activator of transcription pathway as well as via activation of mitogen-activated protein kinases and is known to critically regulate processes such as liver development and regeneration, hematopoiesis, and angiogenesis, which are also determined by hypoxia with the hypoxia-inducible factor 1alpha (HIF1alpha) as a key component. Here we show that treatment of hepatocytes and hepatoma cells with OSM leads to an increased protein level of HIF1alpha under normoxic and hypoxic conditions. Furthermore, the OSM-dependent HIF1alpha increase is mediated via Janus kinase/signal transducer and activator of transcription 3 and mitogen-activated protein kinase kinase/extracellular signal-regulated kinase 1/2 pathways. OSM-mediated HIF1alpha up-regulation did not result from an increase in HIF1alpha protein stability but from increased transcription from the HIF1alpha gene. In addition, we show that the OSM-induced HIF1alpha gene transcription and the resulting enhanced HIF1alpha protein levels are important for the OSM-dependent vascular endothelial growth factor and plasminogen activator inhibitor 1 gene induction associated with several diseases. Conclusion: HIF1alpha levels increase significantly after treatment of hepatocytes and hepatoma cells with OSM, and HIF1alpha contributes to OSM downstream signaling events, pointing to a cross-talk between cytokine and hypoxia signaling in processes such as liver development and regeneration. (HEPATOLOGY 2009.). [less ▲]

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See detailSOCS-mediated downregulation of mutant Jak2 (V617F, T875N and K539L) counteracts cytokine-independent signaling.
Haan, Serge UL; Wuller, S.; Kaczor, Jakub UL et al

in Oncogene (2009), 28(34), 3069-80

Recently, mutations in the gene of Janus kinase 2 (Jak2) were discovered in patients suffering from chronic myeloproliferative disorders (MPD) and leukemia. As suppressors of cytokine signaling (SOCS ... [more ▼]

Recently, mutations in the gene of Janus kinase 2 (Jak2) were discovered in patients suffering from chronic myeloproliferative disorders (MPD) and leukemia. As suppressors of cytokine signaling (SOCS) proteins are potent feedback inhibitors of Jak-mediated signaling, we investigated their role in signal transduction through constitutively active Jak2 mutants. We selected two mutants, Jak2-V617F and Jak2-K539L, found in patients with MPDs and Jak2-T875N identified in acute megakaryoblastic leukemia. We found SOCS family members to be induced through Jak2-V617F in human leukemia cell lines expressing the mutant allele and in stable HEK transfectants inducibly expressing constitutively active Jak2 mutants. SOCS proteins were recruited to the membrane and bound to the constitutively active Jaks. In contrast to wild-type Jak2, the mutant proteins were constitutively ubiquitinated and degraded through the proteasome. Taken together, we show a SOCS-mediated downregulation of the constitutively active, disease-associated mutant Jak2 proteins. Furthermore, a threshold level of mutant Jak expression has to be overcome to allow full cytokine-independent constitutive activation of signaling proteins, which may explain progression to homozygocity in MPDs as well as gene amplification in severe phenotypes and leukemia. [less ▲]

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